Variable resistor



y 15, 1934- J. A. FLANZER ET AL 1,959,097

VARIABLE RES I STOR Filed Oct. 2. 1930 2 Sheets-Sheet 1 JOSEPH A.F'LANZER LESTER L.J 0NES O EMIL REISMAN,

F INNTS I ATTORNEYS May 15, 1934.

VARIABLE RESISTOR Filed 001;. 2.1950 Z SheetS-Sheet 2 JOSEPH A, FLANZER.H3 LESTER L.JONES x" EMIL REISMAN INVENT S.

ATTORNEY J. A. FLA'NZER ET AL ,097

Patented May 15, 1934 UNITED STATES PATENT OFFICE Jones, Oradell,

and Emil Reisman,

Brooklyn, N. Y., assignors to Technidyne Corporation, New York, N. Y. acorporation of New York Application October 2, 1930, Serial No.

14 Claims.

This invention relates to variable resistors, particularly thoseemploying a resistance film coated on an insulation base, and moreespecially to such resistors provided in compact form and having smalloverall dimension.

In copending applications of Lester L. Jones, Serial No. 193,357, filedMay 21, 1927, and Serial No. 350,731, filed March 28, 1929, (sinceissued as Patents 1,836,600 and 1,819,246 on December 15, 1931 and Aug.18, 1931, respectively) there are disclosed variable resistors in whichthe re-- sistance element consists of a thin resistance film coated onan insulation base. The object of the present invention is to generallyimprove the construction and operation of such resistors, andparticularly with a view to providing a compact resistor which isexceedingly small in overall dimension.

The resistance elementconsists of an enameled base, on one face of whichan annular film of resistance material is painted. In order to reducethe overall diameter of the finished resistor, we make the insulationbase in the form of a circular disc which is only slightly larger thanthe desired outside diameter of the resistance film, or, differentlyexpressed, the resistance film is painted closely to the edge of theenameled disc.

It is necessary to provide a terminal contact at one end of theresistance film. In order to make the unit operative as a potentiometer,it is desirable to provide terminal contacts at both ends of theresistance film. As is set forth in the latter of the above identifiedapplications, these terminal contacts may best be provided by paintingthe end of the resistance film with a silver paint. In -order to obtainan outside connection with these terminals they have heretofore beenextended beyond the diameter of the resistance film. In accordance withone of the objects of the present invention, the diameter of thecomplete resistor is not much greater than that of the resistance film,and to fulfil this object and yet provide convenient contact with theterminal contacts, we find it possible and convenient to paint theterminals over the resistance film and to extend the painted terminalsaround the edge of the base and onto the back thereof, at which pointcontact may readily be made with connector lugs projecting from the backof the finished resistor.

As is above indicated, compactness in the present resistor is attained,first, by painting the resistance film close to the edge of theinsulation base, and, second, by painting the silver REISSUED contactterminals around the edge of the base. These. two expedients introduceconsiderable difficulty because of the fact that the insulation base isenameled. The enamel tends to form round surfaces because of itscohesiveness and surface tension. When a sheet of material having squarecut edges is enameled, the enamel tends to bulge at the periphery of thedisc. This makes the resulting base unsatisfactory for receiving aresistance film close to the edge thereof, inasmuch as the slidingcontact will not have a flat surface on which to ride. If the sheetmaterial is made of metal, as is usually the case, additional difficultyarises because the enamel, in tending to round itself, cuts close to andfrequently exposes the sharp corner edges of the metal. This makes thebase unsatisfactory for the application of the silver paint which isextended around the edge and onto the back of the same.

Accordingly, a further object of our invention is to overcome theforegoing difficulties and to make it possible to obtain a moresatisfactory and continuous coating of enamel on a base, with theapplication of fewer or even one coat of enamel. This, we have found, ispossible by rounding the edge of the sheet metal before applying enamelto the same. When the base is rounded in this manner the enamel followsthe natural curve of the edge, and no bulge is formed. A perfectly planesurface results, on which the resistance film may be painted as closelyto the edge thereof as may be desired.

Contact with the resistance film is made by a sliding brush or floatingcontact which slides directly upon the surface of the resistance film.As

has been set forth in the above identified copend- 'ing applications,this contact is preferably made of pure silver in order to takeadvantage of a certain amount of natural lubrication between theresistance film and the silver, and in order to prevent abrasion andwearing out of either the resistance film or the silver. The slidingbrush is preferably formed with a number of individually movable fingersin order, to make good contact over the entire width of the film, andthe effective operation of the brush therefore depends upon it having acertain amount of natural resiliency. A further object of our inventionis to provide a brush contact which will be economical in the use ofsilver, which will possess the advantageous wearing properties of a softmetal such as pure silver, and which, at the same time, will possess theadvantageous springiness of relatively hard resilient metals such asphosphor bronze or of the backing metal, and-thereafter handling thecompound sheet of material as a single sheet of material when runningthe same through the dies which cut and form the sheet material into thedesired shape of the brush.

The brush is pivotally mounted on a rotatable contact arm which is fixedto a rotatable control shaft. This contact arm should be as resilient aspossible, andthis effect may ordinarily be obtained by reason of theradial length thereof be: tween the axis of rotation and the brush. Inthe present resistor, however, in which the entire diameter of the unitmay be exceedingly small, it is desirable that the resilient length ofthe contact arm be made considerably greater than. the effectivesradiusthereof. To fulfill this object we have devised a contact arm which maybe stamped out of a single piece of resilient sheet metal, and l whichcomprsies a central portion which is fixed to the shaft and an outerportion fixed to the central portion at one side thereof, -the slidablebrush being mounted on the. outer portion at the opposite side thereof.This construction makes the resilient length of the contact arm equal tothe diameter, rather than the radius thereof.

Other objects of the present invention are concerned with the provisionof a compact assembly for the finished resistor, and the construction ofthe elements of the resistor so that they may be conveniently assembledto form the completed resistor.

To the accomplishment of the foregoing and such other objects as willhereinafter appear, my invention consists in the resistor elements andtheir relation one to the other as hereinafter are more particularlydescribed in the specification and sought to be defined in the claims.The specification is accompanied by drawings in which:

.Fig. 1 is a perspective view of a finished resistor;

Fig. 2 is a section taken through the same;

Fig. 3' is an exploded view showing the method of assembling theresistor;

Fig. 4 is a rear elevation of the resistance element assembly;

Fig. 5 is a detail section through the resistance element;

Fig. 6 is an elevation of the bearing plate and contact arm assembly;

Fig. 7 is an enlarged section taken in the plane of the line 7-7 in Fig.6;

' Fig. 8 is a section taken in the plane of the line 88 in Fig. 7; and

Figs. 9 and 10 are detail sections illustrative of a feature of ourinvention.

A perspective view of a finished resistor made in accordance with ourinvention is shown in Fig. 1. As is evident from that figure, theresistor comprises a cylindrical body A which may be mounted directlyupon a panel or the like by means of a threaded bushing B. It should benoted that the body A of the resistor is quite small in length, whilethe diameter thereof is no greater than that of the adjusting knob Cwhich itself is relatively small. More specifically, the resistor maysuccessfully be constructed with the body A having a diameter of onlyabout three-quarters ofan inch. and a preferred and popular size is onea potentiometer.

in whichthe diameter of the body A is about one inch. These resistorsare, of course, intended for special use in which size is an importantfactor, and particularly so where the conflicting requirements of smallsize and very high resistance variation must be met. A specific exampleof such use is the mounting of a volume control resistor directly uponthe tone arm of a magnetic pickup for phonographs.

Referring to Figs. 2 and 3, the resistor may be described, generally, ascomprising a cupshaped housing or casing A in which there is housed aresistance element assembly comprising a resistance element D and acontact lug disc E, and on which there is mounted a contact arm assemblycomprising a bearing plate F and a contact arm G carrying a brush H. Thebearing plate F is permanently attached to the casing A by means of asealing ring J. As is evident from an inspection of Fig. 3, theseelements may be assembled together in an exceedingly simple manner bymerely dropping the resistance element assembly D, E into the bottom ofthe housing A, thereafter applying the bearing plate F to the edge ofthe housing, and locking the plate and housing together by means of thesealing ring J.

These elements will next be considered in greater detail. The resistanceelement D employs enamel for insulation. This enamel is ordinarilyapplied to a sheet metal stamping, which is desirable because of theease with which the the surface of the isolantite is not nearly assmooth as that of the enamel, and the surface irregularities may projectthrough thethin resistance film and wear the sliding contact exucessively.

In order to obtain the desired compactness in dimension, the resistancefilm is applied as near to the edge of the. enameled plate as possible.This is evident from Fig. 3, in which it will be observed that theannular resistance film 2 extends quite close to the edge 4 of theresistance element D. Terminal contacts for the resistance film 2 areprovided by painting the ends of the resistance film with silver paintin order to form the terminals 6. Only one such terminal is needed whenthe unit is to be used as a resistor, but it is convenient to provideboth terminals so that the unit may be employed, when desired, as Inaccordance with another feature of the present invention, in order toconserve space, contact is made with the terminals 6 at the back of theresistance element, and for this purpose the terminals are extendedaround the edge and onto theback of the enameled base. This is clearlyevident in Fig. 5 in which it will be seen that the resistance film 2,painted on the enameled base 4, is superimposed by a coating of silver 6which is extended around the edge of the enameled base and onto theopposite side in order to form the terminal face 8.

The nature of the enamel and method of applying and treating the same;the nature of the resistance paint and the method of applying andtreating the same and of adjusting the resistwill 30 at the edge of thesheet 12.

tion, and reference may be made to U. S. Patent No. 1,773,105 issued toLester L. Jones, Alois Schmidt, and Joseph Jones on August 19, 1930, andto the copending applications of Emil Reisman, Serial No. 350,478, filedMarch 28, 1929,

since issued as Patent 1,808,790, dated June 9,

1931, Joseph A. Flanzer and Emil Reisman, Serial No. 393,573, filedSeptember 18, 1929, since issued as Patent 1,881,445, dated Oct. 11,1932, Emil Reisman, Serial No. 393,574, filed September 18,

1 1929, Joseph A. Flanzer, Serial No. 444,614, filed April 15, 1930,since issued as Patent 1,906,846, dated May 2, 1933, and Joseph A.Flanzer and Lester L. Jones, Serial No. 467,832, filed July 14, 1930, aswell as the previously identified copending applications, for detailedinformation on these points.

It has heretofore been the practice to employ a sheet having square cutedges, such as the sheet 12 in Fig. 9. When enamel is applied to such asheet, because of the cohesion and surface tension of the enamel, thereis a tendency for the surface of the enamel to round itself whereverpossible rather than to take sharp corners, and consequently there is adistinct bulge of enamel This bulge forms ridges 14 on the face of thedisc and at the same time cuts the corners of the disc closely, and evenpermits exposure of the same, as at the points 16. Regardless of Whatmaterial the sheet 12 is made from, the bulges l4 introduce a difficultyin as is usually the case, an additional disadvantage arises because thecorners 16 are insufficiently insulated and may tend to short circuitthe silver terminals which are painted around the edge of the enameledbase. These difficulties are overcome by rounding the edge of the sheet12 so as to anticipate the natural tendency of the surface of the enamelto contract. Thus, in Fig. 10, the sheet 12' differs from the sheet 12in having the rounded edge 18, and in consequence of this the enamel 14'is distributed in a uniform layer entirely around the sheet 12. This notonly effects the desired cure of the difficulties above enumerated, but,we have found, possesses the additional advantage of enhancing thenatural covering power of the enamel, so that fewer coats of enamel arenecessary, and even-one coat may be successfully employed on a platerounded, as by swaging.

The connector lug disc E is best shown in Fig. 4.

This disc consists simply of a stamping of very thin insulation, such asbakelite. The outer diameter of the disc is made very slightly largerthan that of the resistance element D, the periphery of which isindicated by the dotted lne The disc, when stamped, is provided with acentral aperture 22 and a plurality of slots 24, 26, and 28, as well asa keyway 30. Connector lugs or soldering lugs 32 are attached to thedisc E by being threaded through the upper slots 26 and 7') along theface of the disc, and thereafter back through the slots 28, the ends 34of the lugs being bent upwardly against the disc in order to anchor thelugs securely in place. The extensions of the silver terminals 8 areformed as shown in order to bring the silver into direct contact withthe flat portion of the lugs 32 lying between the disc E and theresistance element D. The lugs, as well as the contact arm and otherparts subsequently described, are preferably plated with cadmium ortinned so as to prevent poor contact as a result of oxidation ortarnishing.

The connector lug disc E and the resistance element D are preferablypreliminarily riveted together to form a sub-assembly. This is mostconveniently accomplished by a central rivet 36 which may mosteconomically be made in the form of an eyelet. This same rivet may beused to lock an additional soldering lug 38 in place, and the lug may beprevented from turning about the rivet 36 by means of an extension 40,the end of which is passed throughthe slot 24 and bent downwardlyagainst the opposite face of the disc E. This incidentally serves tokeep the resistance element D and the disc E in parallelism, as is bestshown in Fig. 2.

The contact arm assembly is best shown in Figs. 2 and 6. It comprises,generally, a bearing plate F which is rigidly attached to a threadedbushing B. This bushing carries a rotatable shaft 42, at one end ofwhich there is flexibly riveted thereto a rotatable contact arm G whichin turn carries a sliding brush or contact H.

The sliding brush H must be relatively great in width in order tocontact with substantially the full surface of the resistance film. Toinsure good contact at all points along the width of the film, the brushis subdivided to form a plurality of separately movable fingers 44. Theconstruction disclosed in copending application 357,031 previouslymentioned, in which leading and trailing fingers are employed, is notsuitable in the present resistor, due to the small space available, andparticularly the small total length of the resistance film. Accordingly,a single set of contacting fingers is employed, and the configuration ofthese fingers is best shown in enlarged Figs. 7 and 8 which are sectionstaken along the lines 7-7 and 8--8, respectively. In Fig. 8 it will beobserved that the fingers 44 have an open edge 46 and a closed edge 48.The open edge ordinarily makes better contact with the resistance filmthan the closed edge 48, and it is therefore preferable that the fingersbe so related to the resistance element that the open ends 46 aredirected toward the zero resistance terminal of the resistance element.It will also be evident from an inspection of Figs. 7 and 8 that thebrush H is pivotally mounted on the contact arm G by reason of a fulcrumor pivot point 50 being formed in the contact arm G, which point bearsagainst the brush H and permits a universal tilting movement of thebrush so that it may seat itself as flatly as possible on the resistancefilm. The ends of the brush are provided with lugs 52 which are freelyreceived in mating slots 54 in the contact arm. This arrangement doesnot interfere with the desirable free tilting movement of the brush onthe contact arm, but at the same time keeps the brush in proper radialalignment so that the fingers are individually pointed in the the brushnor the film are injuriously abraded even over long periods of wear. Atthe same time, the desired efficient contact of, the brush over the wideresistance film can best be obtained only by the provision of a certainamount of resilience in the contact fingers of the brush. In accordancewith the present invention the desirable properties of pure silver forsoftness, and of phosphor bronze or nickel silver for resilience, arecombined without adding to the complexity of the brush and itsmanufacture. An inspection of Figs. '7 and 8 will show that the brush ismade of two laminations of material. The outer lamination 56 is made ofpure silver, while the inner lamination 58 is made of resilientmaterial, such as phosphor bronze or nickel silver. In manufacture,these sheets of material may be superimposed and pressed together toform, what is for all practical purposes, only a single sheet ofmaterial which may thereafter be fed through the usual dies in order topunch and form the compound sheet" of material into the desired brush.In efiect, the brush is made of pure silver but is provided with abacking spring of resilient material for urging the silver into contactwith the resistance film.

The contact arm G is made of springy material in order to resilientlyurge the brush into contact with the resistance film. Ordinarily thedesired resilience of the contact arm may be obtained as a result of itshaving appreciable length between its center of oscillation, or point ofattachment of the shaft, and the point of mounting of the brush. In thepresent case, however, as is obvious by inspection of the drawings, theradius at which the brush is rotated is so small that no appreciablegive would be obtainablein the contact arm, if constructed in theconventional manner. We have, accordingly, devised the special contactarm, best shown in Fig. 6, which is characterized bythe fact that thecentral portion 60 thereof is rigidly mounted as by riveting to theshaft 42. An outer portion 62 of the contact arm is fixed to the centralportion 60 at one side thereof, as at 64, while the brush H is fixed tothe outer'portion 62 at the opposite side thereof, as at 66. The contactarm may, of course, be stamped from a single sheet of resilientmaterial, and the outer portion 62 may then be enlarged, as at 66, toaccommodate the brush H. It will be evident that in this arrangement thegive of the contact ar'm may take place at the point 66 about the point64, or, in other words, over a length equal to the diameter rather thanthe radius of the contact arm. Furthermore, the construction shownisparticularly resilient, due to the fact that the central portion 60 isitself somewhat resilient, and due to the fact that the joinder betweenthe central portion 60 and the outer portion 62 is yieldable.

The shaft 42 is permanently but rotatably fastened in the bushing B byreason of the shoulders '70 and 72 formed at the ends thereof, theshoulders 72 receiving the contact arm G. The bushing B is forced orpressed into the bearing plate F and is permanently held thereby. Thebearing plate F is circular and has a diameter coinciding with that ofthe outer edge of the casing A. The bearing plate F is'appropriatelyflanged, as at '74, in order to receive the bushing B. A lug or stopmember '76 is struck from the material of the bearing plate F and bentinwardly. This stop member cooperates with a projection 78.

at one side of the contact arm G in order to arrest or limit therotation of the contact arm. An-

other lug may be struck from the opposite side of the bearing plate andbent outwardly, as at 80, in order-.to prevent rotation of the entireresistance unit by mating with a recess or aperture 82 in the panel onwhich the resistor is mounted, this being clearly shown in Fig. 2. Itwill be understood that when rotation of the resistor need not be socarefully guarded against, the lug and aperture 82 may be omitted.

It has already been pointed out that a connector lug 38 is provided onthe resistance element assembly, and that this lug --is not connectedelectrically with the resistance film, but is connected bothmechanically and electrically with the central rivet or eyelet 36. Thelug 38 is intended to be brought into electrical contact withtherotatable arm G, and this contact is most simply and satisfactorilyobtained by forming the contact arm G with a relatively long extension'78, and bending the major portion of the extension over toward thecenter of the contact arm so as to form a resilient contact 90 whichbears against'the rivet or eyelet 36. This resilient engagementincidentally serves to hold the resistance element against the bottom ofthe casing A.

The casing A is preferabiy molded out of bakelite or similar insulation.The bottom is provided with slots 92 for permitting the lugs 32 and 38to pass therethrough. The bottom periphery may also be provided with ashoulder 94 for receiving and supporting the lug holding disc E. A key96 is provided in order to prevent rotation of the resistance elementassembly within the casing. Projections 98 and 100 may be formed at theopen periphery of the casing inorder to fill in the openings left in thebearing plate F when the stop lug 76 and the anchoring lug 80 are strucktherefrom. This mating engagement incidentally causes proper alignmentofthe bearing plate with respect to the casing, and prevents rotation ofthe bearing plate relative to the casing.

An inspection of Fig. 3 shows that the resistance element assembly D, Emay simply be dropped into the casing A, the lugs '32 and 38 passingreadily through the slots 92. The resistance element must be properlyaligned, and is held so by reason of the keyway 96. The contact armassembly F, G, H is next applied to the casing and can be received onlyin proper alignment by reason of the projections 98 and 100. These, itmay incidentally be mentioned, are preferably made different in size soas to prevent the bearing plate F from being mounted 180 degrees out ofproper alignment. The bearing plate is next locked to the casing A bymeans of the sealing ring J. This ring is preferably made of a very thinbrass so that it may readily be rolled downwardly to form the closingflange 102 without appreciably increasing the dimensions of theresistor. The material of the ring is preferably made quite thin for theadditional reason that otherwise, when the nut 104 is tightened on thethreaded bushing B in order to lock the resistor against the panel,there will be a tendency to draw the bearing plate F outwardly and toappreciably distort the same. Of course a shoulder may be formed in thebearing plate to prevent this'distortion, but the present constructionis far simpler and cheaper to manufacture, and no noticeable difiicultyresults because of the thinness of the flange 102 of the sealing ring J.

The lugs 32 and 38 may be shaped as desired, according to the type ofconductor to be soldered or otherwise attached thereto, and the lugs maybe left projecting directly outwardly from the resistor, or they may bebent downwardly in the manner shown in Fig. 1, depending upon the use towhich the resistor is to be put. It will also be understood that thethreaded bushing B may be altered in length to fit the requirements ofany particular installation, and that any appropriate type of knob C maybe afiixed to the end of the shaft 42, as by the use of a set screw, orthe like.

The mode of constructing and assembling the variable resistor of ourinvention, and the many advantages thereof, will, it is thought, beapparent from the foregoing detailed description thereof. The resistoris of the advantageous type employing a resistance film on an insulationbase, which provides an exceedingly smooth and non-microphonicresistance variation the amount of which may be made linear or tapered,as desired. Although the resistor is of the film type, it isnevertheless made so compact in construction that the dimension thereofis considerably smaller than other variable types of resistor notpossessing the advantages of the continuous film resistor. Theinsulation base may be made of enameled sheet metal with no difficultyin enameling the same, although a perfectly plane surface and insulatededge is desired. The sliding brush contact possesses the advantages ofpure silver and the resilience of springy metal such as phosphor bronze.The contact arm is made exceedingly small, and yet has a resilienceequivalent to that of a relatively long arm. A single stamping for thearm incidentally includes a stop member to limit the rotation thereof,and a resilient contact for making electrical circuit therewith and forholding the resistance element in place. The assembly of the unit issimplified by providing sub-assemblies which may be put together withbut little trouble, and without the possibility of mistakes or erroneousalignment in the assembly.

It will be apparent that while we have shown and described our inventionin the preferred forms, many changes and modifications may be made inthe structure disclosed without departing from the spirit of theinvention, defined in the following claims.

We claim:

1. In the manufacture of resistance units comprising an enameled basepainted with a film of resistance material, the method of preventing theformation of a ridge of enamel near the edge of the base which includesrounding the edge of the base before coating the same with enamel.

2. In the manufacture of variable resistance units comprising anenameled metallic disc painted with an annular film of resistancematerial, the method of preventing the formation of a ridge of enamelnear the periphery of the ,disc which includes rounding the edge of thedisc before coating the same with enamel.

' 3. A variable resistor comprising an insulation base, a resistancefilm coated on said base near the edge thereof, and a movable contactarranged for movement over said resistance film, said base comprisingsheet material coated with enamel, the outer edge of said sheet materialbeing rounded prior to the application of enamel thereto.

4. A variable resistor comprising an enameled base, an annularresistance film coated on one face of said base near the peripherythereof, and

a movable contact arranged for movement over said resistance film, saidbase comprising a metallic disc coated with enamel, the outer edge ofsaid disc being rounded prior to the application of enamel thereto.

5. A variable resistor including an insulation base comprising ametallic blank the peripheral edge of which is rounded, and the entiresurface of which is coated with enamel, a film of resistancematerialpainted on one face of said base near the periphery thereof, silverterminals painted over the resistance material at the ends of theresistance film, said terminals extending around the edge ofthe base andonto the back thereof.

6. A variable resistor comprising a metallic disc the peripheral edge ofwhich is rounded, and the entire surface of which is coated with enamel,an annular film of resistance material painted on one face of said discnear the periphery thereof, silver terminals painted over the resistancematerial at the ends of the resistance film, said terminals extendingaround the edge of the disc and onto the back thereof in order to makecontact with connector lugs.

7. A variable resistor comprising an insulation base, a resistance filmcoated thereon, and a movable brush for making sliding contact with saidresistance film, said brush being formed of a laminated piece ofmaterial comprising an outer lamination of pure silver and an innerlamination of relatively resilient material such as phosphor bronze,both of said sheets being similarly shaped and bent into suitableconfiguration to form the desired brush, said configuration ineludingbent holding lugs, whereby no fastening means are needed for securingthe laminations together.

8. A compact variable resistor comprising a generally circularinsulation base, an annular resistance film coated thereon near theperiphery thereof, a fixed metallic contact element at the centerthereof, a rotatable shaft terminating at one side of said base, and arotatable contact arm mounted on the end of the shaft adjacent the base,said contact arm being stamped out of a single piece of resilient sheetmetal and comprising a generally circular central portion fixed to saidshaft, an annular outer portion the diameter of which is approximatelyequal to that of the base fixedto said central portion at one sidethereof, and a brush slidable on the resistance film of the base andpivotally fixed to the annular outer portion of the contact arm at theopposite side thereof, said contact arm further including an extensionfrom the first side thereof bent over from the periphery of the annularmember to a point in axial alignment with the shaft in order to form arelatively long resilient circuit making contact spring for continuouscontact with the aforesaid fixed metallic contact element during therotation of the contact arm.

9. A compact variable resistance of small diameter including acup-shaped housing provided with apertures in the bottom thereof forreceiving connector lugs, a resistance element comprising an insulationdisc, an annular film of resistance material painted around one face ofthe disc near the periphery thereof, and a terminal extending to theopposite face thereof, a connector lug riveted to the center of thedisc, a connector lug in appropriate position for hearing against theterminal, said resistance element being received in said housing, abearing plate arranged to fit on the top of the housing, a rotatableshaft supported therein, a contact arin fixed to said housing, a bearingplate arranged to fit on the rotatable shaft, said contact arm includinga resilient portion for engaging the resistance film and an additionalportion bearing against the aforesaid center rivet of the resistanceelement.

10. A compact variable resistance of small diameter including acup-shaped insulation housing provided with apertures in the bottomthereof for receiving connector lugs, a resistance element comprising adisc coated with enamel, an annular film of resistance material paintedaround one face of the disc near the periphery thereof, and a silverterminal painted over the resistance film at the end thereof and aroundthe edge of the disc and onto the opposite face thereof, a disc ofinsulation riveted centrally to the aforesaid resistance element and toa connector lug, and additional connector lug attached to the disc inappropriate position for bearing against the aforementioned extension ofthe silver terminal, said resistance element and connector lug discbeing received as a unit in the bottom of the top of the housing, arotatable shaft supported therein, and a rotatable contact arm fixed tosaid rotatable shaft, said contact arm including a resilient portioncarrying a brush for engaging the resistance film and an additionalportion bent over to a point opposite the end of the shaft in order tobear against the aforesaid rivet at the center of the resistanceelement.

11. A compact variable resistance of small diameter including acup-shaped insulation housing provided with apertures in the bottomthereof for receiving connector lugs, a resistance element comprising ametallic disc having a rounded edge and coated with enamel, an annularfilm of resistance material painted around one face of the disc nearthe'periphery thereof, and silver terminals painted over the resistancefilm at the ends thereof and around the edge of the disc and onto theopposite face thereof, a thin disc of in: sulation rivetedconcentrically to the aforesaid resistance element and to a connectorlug by means of a central eyelet, additional connector lugs attached tothe insulation disc through slots therein in appropriate position forbearing against the aforementioned extensions of the silver terminals,said resistance element and connector lug disc being received as a unitin the bottom of the housing, a bearing plate arranged to fit on the topof the housing, a rotatable shaft supported center of the resistanceelement so as to make contact with the said eyelet and in order to holdthe resistance element at the bottom of the housing, and a thin metallicsealing ring holding the bearing plate and housing together.

12. A variable resistor including a housing provided with apertures forreceiving connector lugs, a resistance element comprising a metallicdisc having a rounded edge and coated with enamel, an annular film ofresistance material painted around one face of the disc near the.periphery thereof, and silver terminals painted over the resistance filmat the ends thereof and around the edges of the disc and onto theopposite face thereof, a disc of insulation riveted to the aforesaidresistance element and to a connector lug by means of a central rivet,additional connector lugs attached to the insulation disc through slotstherein in appropriate position for hearing against the aforementionedextensions of the silver terminals, said resistance element andconnector lug disc being received as a unit in the bottom of thehousing, and a rotatable contact arm mounted on said housing, saidcontact arm including means contactingwith the aforesaid rivet.

13. A variable resistor comprising an insulation base, a resistance filmcoated thereon, and a movable brush for making sliding contact with saidresistance film, said brush being formed of a laminated piece ofmaterial comprising an outer lamination of a soft highly conductivecontact metal and an inner lamination of relatively harder and moreresilient material, both of said sheets being similarly shaped and bentinto suitable configuration to form the desired brush, saidconfiguration including bent holding lugs, whereby no fastening meansare needed for securing resistor structure, and a central contact forelectrical connection to said arm, said contact arm being stamped out ofa single piece of resilient sheet metal and comprising a central portionfixed to said shaft, an annular outer portion joined to said centralportion at one side thereof, a slidable brush mounted on the annularouter portion of the contact arm at the opposite side thereof, saidcontact arm further including an extension from the first side thereofprojecting outwardly and then reversely bent upon itself to a point inaxial alignment with the shaft for cooperation with the aforesaidcentral contact during rotation of the arm, the outward projectioncooperating with the aforesaid stop means of the resistor in order tolimit the movement of the slidable brush at the opposite side of thearm.

JOSEPH A. FLANZER.

LESTER L. JONES.

EMIL REISMAN.

